1. Field of the Invention
This invention relates to microbially enhanced recovery of oil at elevated temperatures and pressures. More particularly, this invention relates to the selection, isolation and use of aerobic and anaerobic microorganisms, preferably thermophilic microorganisms, which can be maintained at elevated temperatures, pressures, salinity and pH extremes using crude oil and other indigenous matter as a source of energy, perhaps their sole source of energy, for enhanced oil recovery.
2. Background of the Related Art
Oil bearing geological formations often yield crude oil in response to naturally occurring forces, such as gas pressure, gravitational pressure due to the surrounding rock or hydraulic pressure from ground water or steam. The pressure forces the crude oil from the geological formation through a fissure or well at the surface. To increase the recovery of crude oil, pumping is employed. When the level of the oil drops, however, pumping becomes unproductive. In these cases, secondary recovery methods, such as gas, drive or water flooding are utilized to raise the levels of crude oil in the reservoirs.
To facilitate an increase in the yields from these secondary recovery methods, it has long been proposed to subject the geological oil bearing formation to the action of oil-releasing bacteria. This bacterial treatment, called microbial enhanced oil recovery ("MEOR") would be used to supplement the aforementioned secondary recovery methods. The major obstacle that has prevented the implementation of MEOR has been the difficulty in finding, isolating or engineering microorganisms which can survive the harsh variety of environmental conditions present in oil reservoirs. These conditions include temperatures which range from approximately 49.degree. to 90.degree. C., a pH range from approximately 2 to 10, and large variations in brine concentrations, mostly potassium or sodium chloride with average percent total solids ranging from 1.3 to 15.6, as reported by McInerney during the International Conference On Microbial Enhancement Of Oil Recovery, May 16-21, 1982, Bartlesville Energy Technology Center, Bartlesville, Okla. (1983). McInerney observed that magnesium and iron are usually present in most reservoirs at concentrations sufficient to support microbial growth; that sulfur, nitrate and phosphate are not usually present in sufficient concentrations to support microbial growth; and that oxygen concentration are low, indicating anaerobic conditions. McInerney further noted that although different microorganisms grow and reproduce under certain reservoir conditions, for example temperatures from 0.degree. to 100.degree. C., pH from 1 to 10, salinity from 0 to 35%, and pressures up to 1,000 atmospheres, each particular species could only grow at a particular narrow range of conditions. Microorganisms that are naturally present in the reservoir also usually act on the oil to produce undesirable products such as hydrogen sulfide, which are not beneficial to oil recovery.
Microorganisms can be classified in terms of temperature ranges that permit viability. Psychrophiles designate microbial species which grow at a temperature range of from -5.degree. to 22.degree. C.; mesophiles grow from 10.degree. to 45.degree. C.; and thermophiles grow between 40.degree. and 80.degree. C., or higher for extreme thermophiles; see Ljungdahl, "Physiology of Thermophilic Bacteria", Adv Microbial Physiol., 19 149-243 (1979). Similar classifications have been used for the growth of microbial species due to pressure [see Marquis et al., "Microbial Life Under Pressure", in Microbial Life in Extreme Environment, Kushner (ed.), 105-159, Academic Press, N.Y., N.Y. (1978) and Marquis, et al., "Microbial Barobiology", Bioscience, 32, 267-271 (1982)]; pH [see, Langworthy "Microbial Life In Extreme pH Values", Microbial Life in Extreme Environments, Kushner (ed.), 279-317, Academic Press, N.Y., N.Y. (1978)]; and due to salt concentrations [see Kushner, "Life in High Salt and Solute Concentrations: Halophilic Bacteria", Microbial Life in Extreme Environments, Kushner (ed.), 313-368, Academic Press, N.Y., N.Y. (1978)]. While some of the microorganisms described by McInerney referenced above are tolerant to individual environmental effects, none of these microorganisms could withstand the combination of high temperatures and high pressures sometimes rising to over 2,000 psi which are commonly encountered in oil reservoirs.
In the past several years, various university research groups, the National Institution for Petroleum Research, and a number of research groups abroad have laid the ground work for MEOR. See, King and Stevens (Eds), Proc. of the First International MEOR Workshop, Apr. 1-3, 1986, DOE/BC/10852-1 (1986), especially the Lazar article at pages 124-151 of these proceedings, which indicated that MEOR was a promising technology. The conclusion at these workshops was that considerably more research was needed because most field tests were either inconclusive or proved to be outright failures.
An understanding of the chemistry, biochemistry and biogeochemistry of interactions between microorganisms, oils and sedimentary matrices in which these oil deposits occur has been somewhat lacking. Many of the bacteria which have been studied were not tested in the laboratory under reservoir conditions. Nevertheless, the available data suggests several mechanisms for microorganisms to function in MEOR biotechnology. See, Bryant and Douglas, IITRI/NIPER, 449-456, SPE 16284, Society of Petroleum Engineers (1987). These mechanisms include: (1) production of gases (CO.sub.2, H.sub.2, and CH.sub.4) which can increase pressure in the reservoir and reduce oil viscosity; (2) microbial production of low molecular weight acids, which cause rock solubilization; (3) production of biosurfactants which decrease surface and interfacial tensions; (4) microbially mediated changes in wettability; and, (5) production of polymers which facilitate mobility.
It was suggested by Grula in Proc. of The First International MEOR Workshop, Apr. 1-3, 1986, 152-213, DOE/BC/10852-1 (1986) that some of the desirable properties of bacteria to be used in MEOR should include the capacity for large productions of "oil releasing" metabolites (e.g., low molecular weight alcohols, acids, surfactants and gases). These microorganisms should not require expensive nutrients, should be able to survive under anaerobic conditions, and should be capable of withstanding relatively high pressures, temperatures, pH variations and salinities. Additionally, these microorganisms should be easily grown in facilities above ground, remain viable over extended periods of time and be easily transportable. Once placed in the reservoir, these microorganisms should continue to be viable under extreme conditions, and continue their activity upon refeeding. It is to be understood that all of the requirements may not be met by a single type/strain of microorganism and that mixed type/strains may be appropriate for MEOR.
Under certain reservoir conditions, a number of microorganisms have been found to be present in formation waters [see Lazar (1986) supra]. According to Lazar, the usefulness of these bacteria appeared to be limited, since these organisms can only grow in reservoirs of a given depth, salinity, temperature and permeability range. Also, the growth of these bacteria is limited by increases in the concentration of products generated by their own metabolism.
Known thermophilic organisms live under harsh conditions, such as low pH (approximately about .ltoreq.1-3) and high temperatures (up to 110.degree. C.); some are also known to grow under alkaline conditions; [see Brock, Life at High Temperatures, Science 20, 132-138 (1985), and Thermophilic Microorganisms and Life at High Temperatures, 465 pp, Springer Veralag, New York, N.Y. (1978)]. These organisms can use inorganic and organic energy sources (e.g., sulfides, elemental sulfur and ferrous ions). Some of these bacteria are also capable of switching from aerobic to anaerobic metabolism. Further, the natural habitats of these organisms are geothermal brines which allow them to tolerate high salt concentrations. Accordingly, the general properties of thermophilic organisms, although not fully explored, have indicated that they possess a number of the desirable properties for MEOR outlined during the 1986 Workshop, and further verified in recent status reports [see, King, MEOR Technical Status and Assessments Of Needs, DOE/BC/10852-2, DE7-0001227 (1987), and Jenneman, "The Potential for in situ Microbial Applications", Microbial Enhanced Oil Recovery, Developments In Petroleum Science, 22, Donaldson, et al. (eds.), 37-74, Elsevier, New York, N.Y. (1989)].
The use of thermophilic microorganisms to break down complex hydrocarbons in the laboratory environment, has been disclosed in the patent literature. For example, U.S. Pat. No. 2,413,278 to Zobell, discloses the use of bacteria from the genus Desulfovibrio. Some species of this bacteria are disclosed as being active in a temperature range from 70.degree. F. and 180.degree. F. (21.1.degree. C. to 82.4.degree. C.). These bacteria are strict anaerobes, and are inhibited by H.sup.+ ion concentrations lower than pH 6.0. Additionally, there is no disclosure that these microorganisms are functional at anything but ambient pressures. Similarly, in U.S. Pat. No. 2,660,550 to Updegraff et al., the same thermophilic bacteria described in the Zobell patent are used, the improvement being the introduction of molasses in the well water as a source of nutrients and minerals. As in Zobell, the bacteria although described as highly thermophilic, were not tested for growth under high pressures and aerobic conditions.
Additionally, U.S. Pat. No. 2,975,835 to Bond, describes the use of the same bacteria from the genus Desulfovibrio as described above. Bond also discloses the use of other bacteria such as Aspergillus flavus, Bacillus methanicus and Bacillus ethanicus in suitable growth medium. The growth medium containing the bacteria is combined with an aqueous gelling agent and injected under pressure into a well, in order to fracture low permeability oil bearing rock formations. The pressure applied is described as from 0.6 to 1 p.s.i. for each foot of overburden, i.e. for each foot measured from the surface to the formation to be fractured. In an example, a pressure of 900 p.s.i. is applied to fracture the rock. After fracturing, the pressure immediately drops to near ambient pressure. This type of sudden pressure reduction often inactivates the bacteria. Also, the bacteria disclosed by Bond are not described as being capable of growing at high pressures. They are only able to survive in the gel under relatively low pressures (usually less than 1000 p.s.i.) applied for short periods of time until the rock is fractured. Additionally, Bond teaches to maintain the temperature of the gel under 130.degree. F. to avoid destroying the bacteria.
A bacterium useful for cleaving C--S bonds for sulfur removal from dibenzothiophene, resulting in substantially sole products of inorganic sulfate in 2-hydroxybiphenyl is described in U.S. Pat. No. 5,002,888 to Kilbane, II. The preferred microorganism is identified as Bacillus sphaericus ATCC# 53969. The patent describes this bacteria as being able to metabolize the C--S bonds at temperatures from about 20.degree. to 34.degree. C. Accordingly, it appears that this microorganism and method cannot be used in the high pressure and high temperature environment existing in oil reservoirs.
Accordingly, a method for preparing, isolating and utilizing a microorganism which can metabolize crude oils and other high molecular weight hydrocarbons as a source of energy, simultaneously metabolize and solubilize sulfur and organometallic compounds in the crude oils, and emulsify heavy crudes under the extreme conditions existing in oil reservoirs, including temperatures of up to 70.degree.-85.degree. C., high pressures of up to about 2,500 p.s.i., high salinities and extreme pH variations, has not previously been provided.